 In phase one of the HR, the activation of R genes triggers an ion flux, involving an efflux of hydroxide and potassium to the outside the cells, and an influx of calcium and hydrogen ions into the cells.In phase two, the cells involved in the HR generate an oxidative burst by producing reactive oxygen species (ROS), superoxide anions, hydrogen peroxide, hydroxyl radicals and nitrous oxide.These compounds affect cellular membrane function, in part by inducing lipid peroxidation and by causing lipid damage.